> > Hi, Alexander > > > > Thanks for detailed reviewing. > > Likewise! I'll have a look on the entire conversation in a few days... > > > > > > So this isn't going to work with the current recycling logic. The > > > expectation there is that we can safely unmap the entire page as soon > > > as the reference count is greater than 1. > > > > Yes, the expectation is changed to we can always recycle the page > > when the last user has dropped the refcnt that has given to it when > > the page is not pfmemalloced. > > > > The above expectation is based on that the last user will always > > call page_pool_put_full_page() in order to do the recycling or do > > the resource cleanup(dma unmaping..etc). > > > > As the skb_free_head() and skb_release_data() have both checked the > > skb->pp_recycle to call the page_pool_put_full_page() if needed, I > > think we are safe for most case, the one case I am not so sure above > > is the rx zero copy, which seems to also bump up the refcnt before > > mapping the page to user space, we might need to ensure rx zero copy > > is not the last user of the page or if it is the last user, make sure > > it calls page_pool_put_full_page() too. > > Yes, but the skb->pp_recycle value is per skb, not per page. So my > concern is that carrying around that value can be problematic as there > are a number of possible cases where the pages might be > unintentionally recycled. All it would take is for a packet to get > cloned a few times and then somebody starts using pskb_expand_head and > you would have multiple cases, possibly simultaneously, of entities > trying to free the page. I just worry it opens us up to a number of > possible races. Maybe I missde something, but I thought the cloned SKBs would never trigger the recycling path, since they are protected by the atomic dataref check in skb_release_data(). What am I missing? [...] Thanks /Ilias
